This invention relates to apparatus for plugging cylindrical holes provided at an inner wall of a cylindrical container and, more particularly, apparatus for plugging openings of main steam pipes of a nuclear reactor to easily inspect or maintain safety valves, relief valves, and main steam insulation valves, at the time of shutting-down the reactor.
Generally, at a time of a periodical inspection of a nuclear reactor, the reactor is shut down and the inlet openings of the main steam pipes must be plugged. A reactor pressure vessel is then filled with water until the reactor core is entirely submerged under the water to reduce leakage of radioactive rays from the reactor core. Thereafter, safety valves, relief valves and main steam insulation valves disposed in the steam pipes are overhauled and periodically inspected. A conventional apparatus for plugging the inlet opening of the steam pipe will firstly be described hereinbelow in conjunction with FIG. 1.
FIG. 1, reference numeral 1 designates a main steam pipe provided with an inlet opening. Usually four steam pipes are provided. A cylindrical member 2, which has an outer diameter somewhat smaller than the inner diameter of the steam pipe 1, is inserted into the steam pipe 1 opened into a reactor pressure vessel 9. A cylindrical hollow elastic member 3 is disposed in a space between the outer surface of the support member 2 and the inner surface of the steam pipe 1 so that the inlet opening of the steam pipe 1 is plugged at a time when compressed air is admitted into the hollow elastic member 3 through an air feed pipe 4 connected therewith.
Another cylindrical hollow elastic member 5 is disposed between the outer surface of the support member 2 and the inner surface of the steam pipe 1 at the inner end of the support member 2 and is filled with water fed through a pipe 5A thereby to increase the sealing effect of the plugging apparatus. An O-ring 6 is disposed at the outer end of the support member 2 to further increase the sealing effect of the plugging apparatus due to hydraulic pressure caused by the water filled in the reactor pressure vessel 9.
An annular plate 7 is water-tightly welded to the inside wall of the cylindrical support member 2, and to the annular plate 7 is secured a pipe 8 through which the support member 2 is operated or controlled at the upper portion of the reactor core. In a case where it is desired to remove the plugging apparatus from the steam pipe 1, water is supplied into an inner portion 2A of the support member 2 through the pipe 8 to maintain water pressure balance between the steam pipe 1 and the reactor pressure vessel 9. Between the cylindrical members or rings 5, 3 or 6 are disposed detecting means, not shown, for detecting leakage water, thereby to maintain or inspect the sealing condition therebetween.
According to the conventional plugging apparatus described above, it is necessary to independently insert four plugging apparatus into four steam pipes 1 and it takes much time and labor for attaching or removing the plugging apparatus. Moreover, in a case where an operator checks air-tight capability of the safety valves, relief valves, and main steam insulation valves after the inspection or maintenance thereof, although it is required to apply air pressure between the safety valve and the inserted plugging apparatus, the apparatus will be blown into the reactor pressure vessel by counter pressure of the applied air for the reason that the conventional plugging apparatus has no means for withstanding the counter pressure.